Efficiency and yield in a process require a stable gas flow. This gas flow can be measured and controlled by a thermal mass flow controller. There are various external factors in flow control that can have an influence on the measurement accuracy and control stability of mass flow controllers (MFCs). Some examples of external factors are:
These fluctuations can occur due to reduced pressure in a gas cylinder or due to cross-talk between multiple flow controllers. How does Bronkhorst solve these problems, and what solutions do we offer?
Cross Talk typically arises when multiple mass flow controllers are positioned in close proximity in the same pipe, or installed upon the same rail or frame. The line-pressure from a gas regulator is affected by the flow demand of the flow controllers. When the flow instrument is changing its setpoint, it will affect the line-pressure.
Due to this pressure change, the flow measuring section in a conventional flow controller is affected, indicating an incorrect flow measurement that does not represent the actual flow through the MFC. The smaller the nominal flow of the flow controller, the bigger the effect will be to a setpoint change of a larger, parallel installed MFC.
Static pressure compensation is the compensation for slow pressure changes, for example the slowly reduced pressure from a gas cylinder. By integrating a pressure transmitter to the mass flow controller, together with an on-board conversion algorithm, real-time calculation of the actual fluid properties can be performed.
For semi-caloric measurement the density, viscosity, thermal conductivity, and heat capacity are used in the calculation. Under influence of pressure and temperature, these properties change. Thus, actual temperature and pressure are measured and processed, resulting in accurate flow measurement and control stability.
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